At present one of the routes for extending the service life of a cutting tool with a wear-resistant coating made of refractory intrusion phase such as TiC or TiN resides in improving the exploitation charactertistics of the wear-resistant coating itself, in particular its hardness and resistance. To this end, alloying components are incorporated in the coating composition; as such components use is generally made of transition metals of IV-VIa Groups such as zirconium, molybdenum or tungsten.
Known in the art is a process for deposition of a wear-resistant coating onto a cutting tool comprising carbon-containing material [(cf. FRG Pat. No. 1,521,166 Int. Cl..sup.2 C 23 C 17/00, published July 24, 1969)]. This wear-resistant coating contains crystals of tungsten carbide mixed in any ratio with crystals of titanium carbide, vanadium carbide, tantalum carbide or niobium carbide. A coating from mixed crystals is formed as a result of a reaction between transition metals preliminarily deposited on the surface of a cutting tool such as titanium, vanadium tantalum and niobium or alloys thereof and tungsten carbide incorporated in the material of the cutting tool body. This reaction involves the formation of a coating from mixed crystals takes place upon heating of a cutting tool in vacuum or in the atmosphere of a protective gas at a temperature of about 900.degree. C.
These metals are deposited onto the cutting tool surface prior to the formation of a wear-resistant coating by various methods, for example by electroplating or vacuum deposition.
However, a wear-resistant coating can be deposited only on a cutting tool made from hard alloys. For a cutting tool manufactured from an alloy having a lower melting point as compared to hard alloys, e.g. from a high-speed steel, this process is inapplicable.
Furthermore, the number of compositions of thus-produced wear-resistant coating is limited by the reactivity of tungsten carbide which does not substantially react with elements of Groups I--III such as K, Na, Ba, Ca and Al.
Also known in the art is a process for deposition of a wear-resistant coating onto a cutting tool by way of condensation of a substance through ion bombardment. [(cf. Journal "Physics and Chemistry of Material Processing", "Nauka" Publishers, No. 2, 1979, pp. 169-170)]. enabling deposition of a wear-resistant coating not only on hard alloys, but also on tool materials having a lower melting point as compared to hard alloys, i.e. high-speed steels. It involves the following operations: placing a cutting tool in a vacuum chamber, energizing an arc discharge for evaporation of the cathode material, applying a biasing voltage to the cutting tool, heating the cutting tool by bombardment with ions of the evaporated cathode material and formation of a wear-resistant coating through interaction of ions of the evaporated cathode materials with a gas-reactant admitted into the vacuum chamber. In other words, deposited onto the cutting tool is a wear-resistant coating incorporating the components which are present in the compositions of the cathode material and of the gas-reactant. As is known, a cathode is usually made from transition metals of Groups IVa-VIa or alloys thereof, while as the gas-reactant use is made of nitrogen, borane or methane. The thus-produced wear-resistant coating based on refractory intrusion phases such as TiC or TiN has a high hardness and brittleness. To improve the characteristics of the wear-resistant coating, in particular its service life, it is necessary that it have in addition to hardness, plasticity and lubricating properties as well. These properties might be inherent in a coating which incorporates, for example, elements of Groups I-III, as well as Te, Se, Ce, F, Os. However, it is substantially impossible to introduce elements of Groups I-III into the composition of the evaporated cathode material due to their physico-chemical phoperties and specific features of the process of application of a coating by condensation of the substance by ionic bombardment.
Owing to a low melting temperature of elements of these groups, e.g. lithium has a m.p. of 180.degree. C. and sodium--98.degree. C., a fusion of the cathode takes place upon burning of the arc discharge in the vacuum chamber which results in disturbance of conditions of the process for deposition of a coating.
During evaporation of the cathode material the cathode should be cooled with water. For this reason, elements of Group I reacting with water with the formation of an alkali and hydrogen cannot be incorporated into the cathode material, since it creates the risk of an explosion.
Furthermore, it is substantially impossible to make a cathode from a number of materials possessing an insignificant mutual solubility of forming immiscible liquid solutions.
It is also substantially impossible to simultaneously evaporate, by means of an arc discharge, metals incorporated in the cathode composition having ionization potentials essentially differing from one another.
It is neither possible to make cathodes or introduce into the cathode material liquid (mercury) and powder-like (boron, phosphorus) components.
Moreover, it is inadvisable to make cathodes from noble and rare-earth metals such as platinum and lanthanum.
The present invention provides a process for deposition of a wear-resistant coating onto a cutting tool from a carbon-containing material whereby a preliminary treatment of the cutting tool and heating conditions by ion bombardment make it possible to extend longevity of the wearresistant coating and, thereby, the service life of the cutting tool.